The dual capacity compressor is a kind of reciprocating type compressor of which piston stroke and compression capacity changes with rotation directions of a motor and a crankshaft, which is made by means of an eccentric sleeve rotatably coupled with a crank pin of a crankshaft. Since the dual capacity compressor has a compression capacity that can be changed depending on a required load, the dual compressor is used widely in apparatuses which require compression of working fluid, particularly in home appliances operative in a refrigeration cycle, such as a refrigerator, for enhancing an operation efficiency. A U.S. Pat. No. 4,236,874 discloses a general dual capacity compressor, referring to which a related art dual capacity compressor will be described, briefly.
FIG. 1 illustrates a section of a dual capacity compressor disclosed in the U.S. Pat. No. 4,236,874, and FIG. 2 illustrates operation of the dual capacity compressor, schematically.
Referring to FIG. 1, the dual capacity compressor is provided with a piston 7 in a cylinder 8, a crankshaft 1, a crank pin 3 having an axis 3a eccentric from an axis 1a of the crankshaft 1, an eccentric ring 4 coupled with the crank pin 3, and a connecting rod 6 connected between the eccentric ring 4 and the piston 7, as key components. The eccentric ring 4 and the connecting rod 6 are rotatable with respect to each other, as well as the axis 3a of the crank pin. There are release areas 9 in contact surfaces of the crank pin 3 and the eccentric ring 4 respectively, and a key 5 for coupling the crank pin 3 with the eccentric ring 4 in the release areas. The operation of the dual capacity compressor with respect to the compression capacity will be described. As shown in FIG. 2, in the dual capacity compressor, a stroke of the piston 7 is regulated by an eccentricity varied with a position of the eccentric ring 4, wherein, if a large capacity is required, the crank shaft 1 is rotated in a clockwise direction (regular direction) and, if a small capacity is required, the crank shaft 1 is rotated in a counter clockwise direction (reverse direction). In detail, FIG. 2A illustrates a moment the piston 7 is at a top dead center during a clockwise direction rotation, and FIG. 2B illustrates a moment the piston 7 is at a bottom dead center during a clockwise direction rotation, when the stroke Lmax is the greatest because the eccentricity is the greatest. FIG. 2C illustrates a moment the piston 7 is at a bottom dead center during a counter clockwise direction rotation, and FIG. 2D illustrates a moment the piston 7 is at a top dead center during a counter clockwise direction rotation, when the stroke Lmin is the smallest because the eccentricity is the smallest.
However, during the foregoing operation, the crank pin 3 and the eccentric ring 4 are involved in centrifugal forces, respectively caused by their rotation around the axis 1a of the crank shaft, exerting on an extension line between the shaft axis 1a and the pin axis 3a, and between the shaft axis 1a to the a center of gravity of the ring 4a, respectively. Therefore, different from FIGS. 2A and 2B, in cases of FIGS. 2C and 2D, as lines of actions are not on the same line, a local rotating moment is taken place at the eccentric ring 4 with respect to the pin 3 as a product of a vertical distance ‘d’ to the pin 3 and its own centrifugal force, acting in a direction the same with a direction (counter clockwise direction) of rotation of the crank shaft 1. Since the crank pin 3 and the eccentric ring 4 are members that can make relative motion to each other, the rotating moment causes a relative rotation of the eccentric ring 4 in a direction of rotation of the crank shaft 1, releasing the key 5 both from the crank pin 3 and the eccentric ring 4, and leaving the eccentric ring 4 and the key 5 to move in the rotation direction as shown in dashed lines in FIG. 3. Moreover, as shown in FIG. 3 for an example, during clockwise direction operation, a pressure ‘P’ (a pressure of re-expansion of the working fluid) in the cylinder after compression pushes the eccentric ring 4 to a direction of rotation of the crank shaft 1, to cause the eccentric ring 4 to make a relative rotation with respect to the crank pin 3 in a rotation direction of the crank shaft. At the end, such a relative rotation makes operation of the compressor unstable, to fail to obtain a desired compression performance.
In fact, the relative rotation is occurred because the key 5 fails to hold both the crank pin 3 and the eccentric ring, perfectly. The key 5 rolls within the release area whenever the direction of rotation of the crank shaft is changed, to cause serious wear at respective contact surfaces, that shortens a lifetime of the compressor.
Other than the U.S. Pat. No. 4,236,874, there are many patent publications that disclose technologies of the dual capacity compressors, which will be described, briefly.
Similarly, U.S. Pat. No. 4,479,419 discloses a dual capacity compressor provided with a crank pin, eccentric cam and a key. The key is fixed to the eccentric cam, and moves along a track in a crank pin when a direction of rotation of the compressor is changed. However, since the key can not hold both the crank pin and the eccentric cam, positively, the U.S. Pat. No. 4,479,419 also has unstable operation caused by the relative rotation.
U.S. Pat. No. 5,951,261 discloses a compressor having an eccentric part with an inside diameter of bore formed across the eccentric part, and an eccentric cam with another bore with an inside diameter the same with the eccentric part formed in one side thereof. A pin is provided to the bore in the eccentric part, and a compression spring is provided in the bore in the eccentric sleeve. Accordingly, when the bores are aligned during rotation, the pin moves into the bore in the cam by a centrifugal force, to hold the eccentric part and the eccentric cam, together. However, in the U.S. Pat. No. 5,951,261, since the eccentric cam is provided with only one bore therein, the eccentric part and the eccentric cam can hold together only when the compressor rotates in a particular direction. Moreover, an operative reliability can not be secured, since an exact movement of the pin from the eccentric part to the cam through the bores is difficult.
In the meantime, basically, each of the dual capacity compressors described before employs eccentric members, such as an eccentric ring and an eccentric cam, and changes a stroke distance of the piston and the compression capacity with eccentricities of the eccentric members. Because relative arrangements of the eccentric members with members around the eccentric members change with the rotation directions of the compressor, the change of the eccentricity takes place. Therefore, for causing an appropriate amount of change of the eccentricity, it is also important to arrange the eccentric members at required positions accurately before the perfect coupling of the eccentric members.